The present invention relates to coil springs for use in upholstery furniture or cushioned seat and more specifically an apparatus for producing a so-called pocket coil spring structure which comprises rows of enclosures or pockets, each pocket containing therein a coil spring.
Conventional coil springs used in a mattress or chair are joined to one each other by C-shaped rings and are mounted on the base of the mattress or chair. However, joining the coil springs to each other with the C-shaped rings requires a considerable length of time and labor and is thus low in productivity. Also, the conventional coil springs produce unpleasant scratching noises when they are ground by each other is or the C-shaped rings in use, thus degrading the quality of the mattress or chair.
For overcoming the foregoing drawback, a method has been developed, for example as disclosed in Japanese Patent Laid-open Publication 2-20346 (1990), which comprises the steps of accommodating each coil spring in a pocket (enclosure) made of an unwoven material, assembling and placing a row of the pockets in an upright state on a planar base, pressing from above the row of the pockets, applying a spray of an adhesive onto the side of each pocket of the row, and bonding another row of the pockets to the row of the adhesive applied pockets to form a so-called pocket.
In a pocket coil spring structure assembling apparatus embodying such method, the coil springs in the pockets remain held down from above during application of sprays of the adhesive by a spray nozzle. This causes the pockets to be undulated on surfaces thereof as their coil springs are being pressed down. The undulated surfaces of the pockets, the coil spring of which are compressed, are then coated with sprays of adhesive and joined with another row of the pocket coil springs. If crests of the undulated surface of each pocket coil spring where the adhesive is applied fail to meet those of the succeeding pocket coil spring to be joined, the two pocket coil springs may unsuccessfully be joined to each other. This will result in reduction of the quality and life of the pocket coil spring structure. Particularly, when the coil springs have a barrel shape enlarged radially in the middle, their pockets are joined to each other at points and the above predicament will be more critical.
It is an object of the present invention, in view of the above situation, to join rows of pocket coil springs to one another with ease and certainty for forming at a higher efficiency a pocket coil spring structure of improved quality and durability.